Indications and interpretations of pulse oximetry, ABG, and chest radiography.

1. INDICATIONSAND INTERPRETATIONS
OF PULSE OXIMETRY,ABG,CHEST
RADIOGRAPHY
Jithin Jayakumar
20

2.  Pulse oximetry is a non-invasive method of measuring a person’s
oxygen saturation (SpO2).
 Pulse oximeters measures the difference in absorbance of light by
oxygenated and deoxygenated blood and calculate the percentage of
hemoglobin that is oxygenated.
PULSE OXIMETRY

3. Indications
• Very severe pneumonia
• Acute respiratory distress syndrome
• Uncontrolled heart failure
• Asthma or COPD
• Profound shock
• Encephalopathy with respiratory depression
Pulseoximetryisindicatedin;
1. Any situation when hypoxia occurs

4. 2. Monitoring in case of :
• Sleep apnea syndrome
• Oxygen dependent premature baby

5. 3. Other
• Endotracheal intubation
• Procedural Sedation
• Ventilator evaluation
• Assess someone’s ability to tolerate increased physical activity

6. OXYGEN DESATURATION
Oxygen saturation is defined as ratio of O2 content to oxygen capacity of
Hb expressed as a percentage
Desaturation leads to Hypoxemia- a relative deficiency of O2 in arterial
blood
Oxygen saturation will not decrease until PaO2 is below 85mmHg
At Sao2 of 90% PaO2 is already 60mmHg
Rough guide for PaO2 between saturation of 90%-75% is PaO2 = SaO2 –
30
Sa02 less than 76% is life threatening

7. Interpretations
• SpO2 of a healthy person - between 94 % to
100 %.
• In Mild respiratory diseases SpO2 will be 90
% or above.
• If blood oxygen saturation level falls below
90 % consistently, it may indicate some
pathology.
• Supplementary oxygen should be used if
SpO2 falls under 90 % for a long time.

8. • When concentration of Hb is decreased there is a
decrease in total O2 content of the blood, but no
change in O2 saturation. Hence oximetry is not
effective for evaluating anaemia.
• If a patient has abnormal Hb molecule, pulse
oximetry is a poor measure of hypoxemia and may
lead to over treatment, for eg. Sickle cell anaemia.
• Different types of skin pigmentation may change
pulse oximetry results
• In some cases, pulse oximeter may report a high
saturation eg. Carbon monoxide poisoning.

9. Normal 97 to greater or equal to
80
97 to greater or equal to
95
Hypoxia <80 <95
Mild 60-79 90-94
Moderate 40-59 75-89
Severe <40 <75
PaO2 (mmHg) SaO2(mmHg)

11. ARTERIAL BLOOD GASES
Arterial blood gases measurement gives the hydrogen ion
concentration, PaO2 and PaCO2 and derived bicarbonate
concentration in the arterial blood sample.
This is essential for assessing the degree and types of respiratory
failure and for measuring acid-base status.

12. Parameter Normal values
PaO2 greater than 80 mm of Hg
PaCO2 35 to 45 mm of Hg
pH 7.35 to 7.45
HCO3 22 to 26 meq/L
Oxygen content (O2CT) 15 to 22 ml per 100 ml of blood
Oxygen saturation (O2Sat) 95 to 100%

13. How to interpret blood gas abnormalities in respiratory failure?
TYPE 1
HYPOXIA WITH NORMAL OR LOW PaCO2
H+ Normal Normal
Bicarbonate Normal Normal
Causes Acute asthma
Pulmonary edema
Pneumonia
Lobar collapse
Pneumothorax
ARDS
COPD
Lung fibrosis
Right to left shunts
ACUTE CHRONIC

14. TYPE 2
HYPOXIA WITH RAISED PaCO2
H+ Increased Normal or increased
Bicarbonate Normal Increased
Causes Acute severe asthma
Upper airway obstruction
Acute exacerbation of
COPD
Narcotic drugs
Primary alveolar
hypoventilation
COPD
Sleep apnea
Kyphoscoliosis
Ankylosing spondylitis
ACUTE CHRONIC

15. ABG IS DONE IN ORDER TO CHECK;
• Severe breathing problems.
• How treatment for lung diseases is working.
• If you need extra oxygen (Mechanical ventilation)
• Measure acid-base level in blood

16. Complications:
• Feel light headed, fainting, dizziness
• Nausea
• Damage nerve or artery
• Infection
• Air or thrombus embolism.
• Arterial occlusion.
• Local hematoma.

17. CHEST RADIOGRAPHY
 A chest radiograph, called a chest X-ray (CXR), or chest film, is a
projection radiograph of the chest used to diagnose conditions
affecting the chest, its contents, and nearby structures
 Produces images of
• Heart
• Lungs
• Airways
• Blood vessels
• Bones of the spine and chest

19. Indications of chest radiography
• Performed for a broad content of indications;
 Respiratory disease
 Cardiac disease
 Haemoptysis
 Suspected pulmonary embolism
 Investigation of TB
 Pneumothorax
 Suspected metastasis
 Trauma
 Chronic dyspnoea

20. The images seen on a chest radiograph results from the differences in the materials in the
body.
The hierarchy of relative densities from least dense(black) to most dense(white).
Four major groups of chest radiographs
• Posterior-anterior or PA view
• Lateral view
• Anterior-posterior or AP view
• Lateral Decubitus

21. PA view
• The posterior-anterior view is the standard frontal chest view
• The X-ray beam traverses the patient from posterior to anterior
• Performed standing and in full inspiration
Advantage
• Excellent visualization of mediastinum and lungs
Disadvantage
• Patient must be able to stand erect

23. AP view
• The antero-Posterior erect view is an alternative frontal view
to the PA view
• The X-ray beam traverses the patient from anterior to
posterior
• AP supine view is a further alternative frontal projection
technique often used in trauma patients or who cannot sit up
Advantage
 More convenient for sick patients
Disadvantage
 Mediastinal structures may appear magnified

25. Lateral view
• The lateral view of the chest is performed erect left lateral and
labelled with the side closest to the cassette
• It allows for localization of suspected chest pathology when assessed
in conjunction with a PA view
• Examines the retro-sternal and retro-cardiac spaces
• It allows assessment of the posterior costo-phrenic recesses.

27. Lateral Decubitus Position
• The patient lies on either the right or left side rather than
in the standing position as with a regular lateral
radiograph.
• Often useful in revealing a pleural effusion that cannot be
easily observed in an upright view, as the effusion will
collect in the dependent position

29. OTHER IMAGINGS
 Computed tomography or CT
• Computed tomography gives the detailed images of the pulmonary parenchyma, mediastinum , pleura and bony
structures.
• High resolution thin section scanning provides detailed imaging of the pulmonary parenchyma and is particularly useful in
assessing the diffuse parenchymal lung diseases.
 Positron emission tomography or PET
• PET scanners employ the radiotracers F-flurodeoxyglucose to quantify the rate of glucose metabolism by cells.
• PET is useful in the staging of mediastinal lymph nodes and distal metastatic diseases in patients with lung cancer and
other pulmonary diseases.
 Magnetic resonance imaging or MRI
• It is helpful in differentiation of benign from malignant pleural disease and in delineating invasion of the chest wall or
diaphragm by tumour.
 Ultrasound

31. THANK YOU